Re: [PATCH] staging: rtl8723bs: fix potential speculative cpu oob read

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Apr 29, 2026 at 02:45:20PM +0200, Linus Probert wrote:
> On 2026-04-29 13:31:46+02:00, Greg Kroah-Hartman wrote:
> > On Wed, Apr 29, 2026 at 01:10:16PM +0200, Linus Probert wrote:
> > 
> > > Fixes potential speculative cpu oob read in os_intfs.c by guarding the
> > > index with array_index_nospec.
> > > 
> > > Fixes smatch warning:
> > > warn: potential spectre issue 'rtw_1d_to_queue' [r]
> > 
> > Is this value controlled by a user?  Or is it just a normal operation
> > that happens that is not controlled?  In other words, can a user
> > manipulate this directly to be out of range?
> > 
> > thanks,
> > 
> > greg k-h
> 
> To my understanding, yes. Which is somewhat limited due to being rather
> new to kernel code and not having access to this hardware. The priority
> is extracted from ip header which can be user controlled.
> 
> However, looking closer at the execution before I see that in both cases
> bounding is performed on the value as follows:
> 
> 	dscp = ip_hdr(skb)->tos & 0xfc;
> 	prio = dscp >> 5;
> 
> So my change here adds no additional security. The smatch warning is a
> false positive. It only warned on one of the cases. Most likely because
> the bounding happened in a function call and it only sees the u32.
> 
> Some quick LLM research told me this (in my own words but have not
> verified extensively):
> 
> The case where the bounding is performed in a function call could be
> susceptible to *Spectre v4 (Speculative Store Bypass)*.
> But the fix I applied here only applies to v1 so no additional security
> on that front either.
> 
> This is probably best to NAK unless we just want to remove a false
> positive smatch warning. But I personally don't agree with that.

Yes, let's fix the tool instead.  The '&' above shows that this is not
really a spectre issue that you can actually trigger.

thanks,

greg k-h